Marine ecosystems have entered the Anthropocene

Sampling of foraminifera found in a sediment core from the Caribbean, dating back to before the Industrial Revolution. CREDIT MICHAL KUCERA

Anthropogenic climate change and ocean acidification resulting from the emission of vast quantities of CO₂ and other greenhouse gases pose a considerable threat to ecosystems and modern society. Planktonic foraminifera are a group of marine zooplankton that made their first appearance in the Late Triassic. Although, identifying the first occurrence of planktonic foraminifera is complex, with many suggested planktonic forms later being reinterpreted as benthic. They are present in different types of marine sediments, such as carbonates or limestones, and are excellent biostratigraphic markers. Their test are made of  globular chambers composed of secrete calcite or aragonite, with no internal structures and different patterns of chamber disposition: trochospiral, involute trochospiral and planispiral growth. During the Cenozoic, some forms exhibited supplementary apertures or areal apertures. The tests also show perforations and a variety of surface ornamentations like cones, short ridges or spines. The phylogenetic evolution of planktonic foraminifera are closely associated with global and regional changes in climate and oceanography.

John Murray, naturalist of the CHALLENGER Expedition (1872-1876) found that differences in species composition of planktonic foraminifera from ocean sediments contain clues about the temperatures in which they lived. The ratio of heavy and light Oxygen in foraminifera shells can reveal how cold the ocean was and how much ice existed at the time the shell formed. Another tool to reconstruct paleotemperatures is the ratio of magnesium to calcium (Mg/Ca) in foraminiferal shells. Mg²⁺ incorporation into foraminiferal calcite  is influenced by the temperature of the surrounding seawater, and the Mg/Ca ratios increase with increasing temperature.

Planktonic foraminifera from the Sargasso Sea in the North Atlantic Ocean. (Photograph courtesy Colomban de Vargas, EPPO/SBRoscoff.)

Analyzing previously collected sediment samples from over 3,500 sites around the world’s ocean, researchers found that the composition of the planktonic foraminifera has changed significantly since the pre-industrial period. The shifts in planktonic foraminifera are indicative of a more-general phenomenon across marine ecosystem, with zooplankton communities shifting poleward by an average 374 miles as a result of warming ocean temperatures.

Human activity is a major driver of the dynamics of Earth system. After the World War II, the impact of human activity on the global environment dramatically increased. Ocean warming reduces the solubility of oxygen, and raises metabolic rates accelerating the thermal stratification.

References:

Jonkers, L., Hillebrand, H., & Kucera, M. (2019). Global change drives modern plankton communities away from the pre-industrial state. Nature. doi:10.1038/s41586-019-1230-3